Whilst the invention relates to a mooring device for releasably securing and retaining in position a large object in relation to a nearby second large object, it will be described with reference to mooring devices for docking and undocking a vessel. However, it will be understood that the invention is not limited solely to such example.
The use of robot-like mooring devices has been proposed to reduce the labour intensity, hazards and time taken by using the traditional mooring lines. These devices should be capable of restraining movement of the ship in response to winds, currents, shifting tides, movement of the ship due to the addition or removal of cargo, and the like.
An example of such a device is shown in WO91/14615, which describes a mechanism with a prehensile assembly for engaging a bollard on the vessel. A disadvantage of this type of system is that the vessel must be specially adapted. Further, precision is required to align the two coupling components. The prehensile assembly is not adapted to be quickly disengaged during the departure process.
A known system of the applicants employs a mooring arm mounted within a ship to one end of which a vacuum cup is fixed. During mooring, the vacuum cup protrudes through an opening in the hull of the ship and attaches to a bearing plate. The bearing plate is fixed to the dock, but able to rise and fall freely relative to it. Such a system is significantly more efficient than the traditional mooring process but because of the bearing plate, it is only suited to applications where the ship has a dedicated dock. In addition, other means are provided for securing the vessel accurately in the fore and aft direction with respect to the dock. Where such is not the case, this inability to absorb forces acting on the vessel in the fore and aft direction and the necessity to provide a means of raising and lowering the dock mounted attachment plate is a disadvantage of this known system.
U.S. Pat. No. 3,974,794 illustrates an alternative dock mounted system which is able to handle a range of different vessels, with no modification to the vessel being necessary, since the vacuum cups bear on the ship's hull. Hydraulic cylinders are used to rotate the vacuum cup fixed to a dock to conform to the shape of the hull.
U.S. Pat. No. 3,463,114 describes a mooring device with a buffered telescopic boom fitted with a vacuum cup for engagement with the hull of a ship. The boom is fixed in vertical guides and it is allowed to rise and fall with the ship when fastened thereto.
In both of these systems (in U.S. Pat. Nos. 3,463,114 and 3,974,794) the ship is rigidly fixed to the mooring station in the longitudinal direction with respect to the ship, consequently the mooring device is subject to deleterious impact loads in this direction. Neither system may be used to control the position of the vessel in the fore-and-aft direction.
DE 2557964 illustrates a fending device with two dimensional movement and impact absorption. However there is no means for mooring a vessel, nor retain the moored vessel against a dock.
Generally, there are three degrees of freedom of the position of a floating vessel: fore-and-aft, rise-and-fall, and athwart-ship (and there are three degrees of freedom of its orientation or rotation: roll, pitch and yaw). When mooring a vessel, particularly a massive vessel, it is desirable to have a degree of compliance in the mooring device, to avoid impact loads which may occur in any direction. Additionally, when loading a vessel for example, it is often desirable to control and to vary the fore-and-aft position of the vessel relative to the dock, as well as to control the athwart-ship position.
It is an object of the present invention to provide a mooring device which automatically positions a first large object relative to a nearby second large object, with precise control of both the fore and aft and the athwart-ship position of the first object with respect to the second object, and which device reliantly buffers the mooring forces exerted between the two objects.
It is a further object of the present invention to provide a mooring device which provides increased control over the movement of the first large object relative to the second object, as compared with mooring devices known in the art.
It is a further object of the present invention to address the foregoing problems in respect of positioning a first large object relative to a second large object or to provide the public with a useful choice.
Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.